Thompson & Morgan
How to grow tomatoes

Growing tomatoes

Introduction

Tomatoes are tender annual plants in most regions, but are classed as short lived perennials in the tropics. The ripe fruit colour may be anything from red and orange right through to white and green ones. In shape they range from tiny currant sized fruit up to the giant beefsteak variety. Tomatoes grow best at a temperature of 21 - 24C (70 - 75F). They will not grow well if kept above 27C (81F) or below 16C (61F). They will not tolerate frost. Tomatoes also require a high light intensity.

Sowing the Seed

The tomato seed is quite easy to handle, so it can be spaced out and covered with about 1.5mm (1/16in) of compost. The seedlings generally germinate in about 7 to 14 days at a temperature of around 21C (70F). For the best sowing times, see the recommendations in 'greenhouse' or 'outdoor' cultivation below. Pot on when large enough to handle without touching the stem. Just handling the leaves, transplant them carefully into 7.5cm (3in) pots. If only a few plants are required sow two seeds into a 7.5cm (3in) pot and after germination remove the smaller plant. Take care not to let the plant and seedlings get cold. Frost, cold winds and draughts will cause the plants to turn blue and in most cases die. If you live in a cold area wait a few weeks extra until the air temperature has risen a bit more. Check the compost at all stages for dryness. This is vital in the germination stages as drought can cause poor germination or failure to germinate at all. If this is the case, add a little clean water from below, being careful not to over water. Too much water can kill seedlings, as it can spread "damping off fungi" and encourage other moulds and diseases.

Greenhouse Cultivation

For greenhouse tomatoes first pick a recommended variety such as 'Santa', 'Matador', 'Sungold', 'Money Maker' or 'Supersteak'. Sow as directed on the individual seed packet. This is generally from late December/early January onwards and in 7.5cm (3in) pots.

Plant the young plants when they are about 15-20cm (6-8in) tall and the flowers of the first truss are just beginning to open. If you are planting into your greenhouse border make sure you have dug in plenty of garden compost or peat during the winter. If you have used the border before for tomatoes, it is better to change the soil or sterilise it before using it for tomatoes again. This will help avoid soil pests and root diseases becoming a problem. Just before planting, rake in a general purpose fertiliser. If you are going to use a growbag or pot remember they will require a lot more watering and care. Plant approximately 45cm (18in) between the plants and 75cm (30in) between the rows. In a growbag, generally plant no more then two plants per bag.

Outdoor Cultivation

For growing tomatoes outside, first pick a recommended variety such as 'Gardeners Delight', 'Sungold', 'Money Maker' or 'Sweet 100' or try 'Tumbler' in a flower pouch or hanging basket.

Wait until approximately 6-8 weeks before the last frost is forecast and sow as directed on the individual seed packet in 7.5cm (3in) pots.

When all risk of frost has past and when the plants are about 15-20cm (6-8in) tall and the flowers of the first truss are just beginning to open, you can plant them out. If you are planting into your border make sure you have dug in plenty of garden compost or peat during the winter. Just before planting, rake in a general purpose fertiliser. If you are going to use a growbag or pot remember they will require a lot more watering and care. Plant approximately 45cm (18 in) between the plants and 75cm (30in) between the rows. In a growbag, generally plant no more than two plants per bag

Training Plants

How to train or when to pick your fruit will depend on the varieties and types of tomatoes grown. Cordon (indeterminate) varieties will need side shooting, determinate varieties may stop flower production after several trusses, but upward growth can be carried on by training up the topmost side shoot. Bush varieties remain low and need no side shoot removal. See individual seed packets for further information. Tomatoes require a lot of water and feed to get the best fruit. Water little and often for the best results. Feed with a general liquid feed until the first truss is formed then alternate with a high potash feed. This will encourage more flowers and fruit.

Pests and Diseases

Most tomato fruit problems are caused by irregular watering. 'Blossom End Rot' (dark patch at the base of the fruit, more common if the plant is grown in a growbag), 'Blossom Drop' (flower bud falls off), 'Dry Set' (fruitlet growth stops when the fruit is the size of a match-head), and 'Fruit Splitting'. The key is to give the plant an even, regular amount of water. Try also to water around the base of the plants, misting the flowers will also help to increase the humidity and give better pollination results. Too much water too late tends to be the problem in most cases, especially with plants grown in pots and growbags.

Other problems tend to be caused by too much direct sunlight. This can be more of a problem. Tomatoes have to have lots of sun to grow well, but to much can cause blotches, scalds or spots on the developing fruit, even the dreaded 'Greenback' is caused by too much sunlight. If this is a problem increase the 'potash' in the plants' feeding regime and use fleece or shading as a cover in the hottest part of the day.

As with most plants look out for green and white fly, both can spread viruses. Spray with are recommended proprietary spray as soon as any pest is noticed. Seed cannot carry viruses: mottling, leaf distortion and stunted plant growth will be caused by sap sucking pests. They can spread viruses so keep an eye for them.

If leaf yellowing starts on the older leaves and moves upwards it may not be a virus but a deficiency of magnesium. It is common, but general feeding will not help. Use a multi tonic or special magnesium feed if required.

If you believe your tomatoes do have a virus, the plant or plants must be removed and destroyed. Avoid handling other tomatoes, or using the same tools on your tomatoes until you and the tools have been thoroughly washed.